The subject of the invention is a float for a fill level sensor, comprising a fuel-resistant plastic, an expanding means and/or a filler. Floats of this type are used in fill level sensors in fuel tanks of motor vehicles.
Floats made of fuel-resistant material are generally known. On account of the low density of fuel, floats must have a particularly low density. An additional difficulty is that, for the most part, lever-type sensors are used as fill level sensors. In the case of a fill level sensor formed as a lever-type sensor, the float is fastened to a lever wire. Also arranged on the lever wire is a sliding contact, which slides over a resistor network. The float must consequently have a much lower density than the fuel, since it has to compensate not only for its own weight but also for the weight of the lever wire. In the case of a fuel density of approximately 0.7 g/cm3, floats of this type must therefore have a density of less than 0.5 g/cm3.
A material which is both fuel-resistant and has an adequately low density is nitrophyl. Nitrophyl is a plastic containing sulfur. The disadvantage of nitrophyl is its complex production, which necessitates stringent requirements with regard to environmental protection because of the sulfur content.
Other known fuel-resistant materials are POM (polyoxymethylene) and PA (polyamide). However, the production of foamed floats from these materials is extremely complex. A further disadvantage is that foaming produces an open-cell foam, the cells of which are interconnected and therefore become flooded with fuel if the outer layer of the float is damaged. As a result, the float loses its buoyancy, which leads to failure of the fill level sensor.
It is also known to produce floats as hollow bodies from POM or PA. These floats have the disadvantage that, when they are used in a motor vehicle, the shell of the float can be damaged as a result of the dynamics of the vehicle movement. The leakage causes the float to be flooded, whereby it loses its buoyancy, which leads to failure of the fill level sensor. Floats comprising hollow bodies have therefore been unable to become widely adopted as fill level sensors in motor vehicles.